1. Field of the Invention
The present invention generally pertains to pre-inerting apparatus and a method for preventing an incipient explosion of large volume of contained flammable fuels. The apparatus of method employ the use of non-ozone depleting hydrofluorocarbon agents to preclude an explosion from occurring.
2. Description of the Prior Art
Early detection and avoidance of incipient explosions has become a necessity in various industries in order to prevent catastrophic damage to physical facilities and injury to workers. Explosion mitigation is especially important in environments where large volumes of contained flammable fuels are present. Electric transformers are particularly susceptible to violent explosions primarily because the transformers are filled with isolating oil, and must handle high electric voltages. Having a flash point near 140° C., transformer oil is generally not flammable at moderate temperatures (40°–60° C.). However, due to aging and impurities of the oil, strong transients or other external impacts, a short-circuit and subsequent electric arc may take place inside a transformer. During the electric arc, the relatively large oil molecules are cracked into primarily hydrogen and acetylene gas. The gas volume generated is typically on the order of 0.05–0.10 m3 per MJ of arc energy. This gas volume creates very high pressure within the transformer which may lead to failure of the transformer casing. When the transformer casing fails, the escaping flammable gas also generates sprays of oil into the transformer room thereby creating a flammable atmosphere, which may ignite in the presence of a sufficiently strong ignition source.
Environmental detection systems such as disclosed in U.S. Pat. No. 4,977,527, which is incorporated by reference herein, have been developed in order to detect conditions that can result in the development of a hazardous atmosphere. The detection system initiates operation of mitigation systems that interrupt and terminate the propagation of flame by chemical and physical methods. Such systems may also reduce the reactivity of the flammable material thereby reducing the flame speeds and explosion pressures. In order to accomplish these objectives, explosion suppression systems have generally employed rapid release of a suppressing agent such as bromochlorodifluoromethane (Halon 1211) or bromotrifluoromethane (Halon 1301), hereafter collectively referred to as Halon, into the space surrounding the transformer upon detection of a hazardous condition which may lead to an explosion.
While effective in explosion suppression and mitigation, Halon because of its bromine and/or chlorine content exhibits significant ozone depletion potential. In view of recent environmental treaties such as the Montreal and Kyoto Protocols, the use of Halon is being phased out. Therefore, there exists a real and unfulfilled need for a mitigation system for use in preventing large volume contained flammable fuels from exploding and that does not employ agents which present an ozone depletion problem.